Gas separation processes using adsorbent beds are well known in the art. Typical adsorption-based processes include those where a gas component within a multi-component feed gas is selectively adsorbed. Of particular interest are cyclic processes wherein the adsorbed gas is removed from the adsorbent material in a reversing gas flow such as pressure swing adsorption (PSA), vacuum swing adsorption (VSA) and vacuum pressure swing adsorption (VPSA) processes. These processes have evolved significantly over the last few years with improvements being made to the adsorbent materials, the adsorbent beds, and the overall process parameters and controls. Costs for the construction and operation of such plants are constantly being driven lower by competitive market pressures and it has become paramount to reduce the costs associated with designing, building, transporting and operating such plants by decreasing bed sizes and standardizing components. Modular and compact adsorbent bed structures are desirable to reduce the adsorbent material inventory; the size of the plant equipment, such as process vessels and surge tanks, and the overall plant footprint including the skid dimensions. Smaller skids reduce transportation and installation costs.
However, it is generally difficult to reduce the size of adsorbent bed structures without also significantly reducing the plant throughput. Modifications in the bed geometry and process parameters bring additional challenges, such as in proper design of bed or vessel shapes, proper distribution of gas flow, management of void volumes, adsorbent loading and containment constraints, and operation of the plant components at faster rates. Shallow beds (those having decreased bed depth) operate at faster cycles.
It is therefore desirable to design new adsorbent bed systems for use in adsorption-based gas separation processes that is modular and smaller in size; require lower fabrication costs; are easier to transport; have less maintenance and repair requirements; and are easier to load with adsorbent material. It is equally important to design adsorbent bed systems that, while being smaller or at least having smaller foot prints, do not negatively affect the process flow, cycle speed, rate and volume of throughput, and overall power requirements of the process.
U.S. Pat. No. 6,533,847 discloses an adsorption bed arrangement to remove airborne contaminants with a plurality of V-shaped adsorption elements having two layers of adsorbents, a housing, and a gasket member.
U.S. Pat. No. 6,802,889 discloses a rapid cycle PSA system, process and apparatus designed for low void volumes, relatively short bed lengths and fast cycles, and use finer adsorbent particles. This unit has small product throughputs and an aspect ratio (L3/V bed) of less than 10, where L is the bed depth and Vbed is the bed volume.
U.S. Pat. No. 7,122,073 discloses a low void pressure swing adsorption system comprised of at least one hermetically sealed vessel containing an adsorbent. The void volume of the inlet and outlet are limited to less than 20% of the adsorbent bed volume.
U.S. Pat. No. 4,969,936 discloses a gas filtration system with a plenum having an inlet, an outlet, a top, and bottom and a V-shaped housing within the plenum chamber with a plurality of apertures for permitting the flow of gas. The filter system has a modular design for filtering large volumes of air.
U.S. Pat. No. 6,436,175 discloses a modular adsorption PSA or VPSA plant comprising one or more transportable cargo containers which hold the various adsorbent beds and pumping apparatus which comprise the plant. The plant is designed for small absolute pressure swings not exceeding 3 bar absolute and at close to ambient pressures (i.e. low pressures adsorption processes). This patent further teaches details of a rectangular vessel apparatus that confines a single adsorption bed.
None of the prior teachings describe the modular compact design of the present invention.
Significant capital cost savings can be achieved using a modular and/or compact adsorbent bed structure in an adsorption-based gas separation plant. For the purposes of the present invention, the term “modular” means reconfiguring a given frontal flow area of a conventional bed into smaller more manageable sections that fit into a housing wherein each bed unit or module is easier to load adsorbent material into, easier to handle and/or replace in the housing, and generally provide greater flexibility in design of the overall adsorption bed structure. Likewise, the term “compact” in the present invention refers to sections or units which provide intensification of the process by decreasing the adsorbent volume required for a given feed flow (by decreasing the bed depth) when cycling the process at a faster rate. In the present invention, a conventional packed bed in a gas separation plant is replaced with a plurality of modular adsorbent bed units. Individual modular adsorbent bed units, containing the adsorbent material, are combined to construct a fully sized adsorbent bed structure or vessel having the size and dimensions required for the particular plant requirements. When the modular adsorbent bed units are also made compact, then additional savings and design flexibility are possible due the reduced amount of adsorbent material required.
One benefit of the present invention, depending on the particular modular units employed, is that the total capacity of the adsorbent bed structure can be increased or decreased simply by including more or less modular adsorbent bed units, i.e. plants of different production capacity require the same general adsorbent bed structure but with the number of modular adsorbent bed units selected according to the feed and product flows desired. Such modular and/or compact beds also allows for greater flexibility in matching the adsorbent bed requirements to the specific adsorbent material efficiency and the output requirements of the particular plant.
The present adsorption bed structure also brings together the benefits of a modular compact design utilizing low inlet void volumes, large bed frontal areas, and short bed depths (transfer lengths). It brings together these factors into a modular and scalable adsorbent bed and vessel design, requiring decreased adsorbent inventory, smaller plant equipment and hence, smaller dimensions. The compact configuration also provides higher capacity of product per unit volume of adsorbent material (i.e., increased adsorbent utilization) as compared to that obtained from a conventional packed bed. The present invention may substantially reduce the pressure drop in the adsorbent bed by optionally providing a very large flow area (frontal area) combined with shorter bed depths facilitating faster cycles in the preferred cyclic processes.